linux-kernel - Re: [PATCH 1/2] Revert "vmalloc: back off when the current task is killed"

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Message-Id: <201710050642.JJI34818.QFSHJOMOtFOLFV@I-love.SAKURA.ne.jp>
Date:   Thu, 5 Oct 2017 06:42:38 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     hannes@...xchg.org
Cc:     akpm@...ux-foundation.org, alan@...yncelyn.cymru, hch@....de,
        mhocko@...e.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 1/2] Revert "vmalloc: back off when the current task is killed"

Johannes Weiner wrote:
> On Thu, Oct 05, 2017 at 05:49:43AM +0900, Tetsuo Handa wrote:
> > On 2017/10/05 3:59, Johannes Weiner wrote:
> > > But the justification to make that vmalloc() call fail like this isn't
> > > convincing, either. The patch mentions an OOM victim exhausting the
> > > memory reserves and thus deadlocking the machine. But the OOM killer
> > > is only one, improbable source of fatal signals. It doesn't make sense
> > > to fail allocations preemptively with plenty of memory in most cases.
> > 
> > By the time the current thread reaches do_exit(), fatal_signal_pending(current)
> > should become false. As far as I can guess, the source of fatal signal will be
> > tty_signal_session_leader(tty, exit_session) which is called just before
> > tty_ldisc_hangup(tty, cons_filp != NULL) rather than the OOM killer. I don't
> > know whether it is possible to make fatal_signal_pending(current) true inside
> > do_exit() though...
> 
> It's definitely not the OOM killer, the memory situation looks fine
> when this happens. I didn't look closer where the signal comes from.
> 

Then, we could check tsk_is_oom_victim() instead of fatal_signal_pending().

> That said, we trigger this issue fairly easily. We tested the revert
> over night on a couple thousand machines, and it fixed the issue
> (whereas the control group still saw the crashes).
>